Humans stereoscopically recognize an object by using a difference (parallax) between an image caught by the right eye and an image caught by the left eye. The rotational movements of the eyeballs change the angle of vergence, and humans recognize this as a distance to an object. The angle of vergence is an angle formed by two line's of vision which cross each other.
When two two-dimensional images for the left eye and the right eye, which have a parallax therebetween, are prepared by using characteristics of the eyes of humans, and then separately projected on the left eye and the right eye, the distance to an object is deluded due to the angle of vergence. This gives humans stereoscopic perception. Here, the parallax is a difference between an image for the left eye and an image for the right eye.
An image obtained by displaying an image for the left eye and an image for the right eye is called a stereoscopic image. An image obtained by preparing a plurality of images for the left eye and a plurality of images for the right eye and continuously changing the prepared images is called a stereoscopic video. Moreover, an apparatus that can display the stereoscopic video is called a stereoscopic video display apparatus.
Further, a stereoscopic video display apparatus has been proposed which alternately displays images for the right eye and images for the left eye on a display in such a manner that a parallax exists therebetween by using shutter glasses in which a pair of left and right lens units is alternately switched between a perspective state and a light shielding state. This apparatus does not require a switching operation of the shutter glasses because the left and right lens units are controlled to be alternately switched between the perspective state and the light shielding state in synchronization with timing at which the images for the right eye and the images for the left eye are alternately switched (for example, refer to Patent Document 1).